The present invention relates to a device for cooling the distribution chute of an installation for charging a shaft furnace, comprising a fixed feed channel disposed vertically in the center of the head of the furnace, a rotary collar mounted coaxially around the feed channel, a fixed outer casing mounted coaxially on the outside of the collar and delimiting laterally with the latter a substantially annular chamber, this chamber being separated from the inside of the furnace by means of a cage securely attached to the rotary collar, a distribution chute mounted in a pivoting manner in the rotary cage, a driving means for causing the collar and the cage to turn, as one, around the vertical axis of the furnace and of the feed channel, two drive casings disposed diametrically opposed in the chamber and rotating with the rotary cage about the vertical axis, these casings acting on the suspension shafts of the chute so as to cause the pivoting of the latter, an annular feed tank secured to the upper edge of the rotary collar and whose outer and inner concentric walls slide in an upper fixed plate through which passes at least one pipe for admission of a cooling fluid feeding the annular tank.
A charging installation of this kind is described in U.S. Pat. No. 3,880,302, incorporated herein by reference, which is directed to bell-less charging installations, currently the most widely used type of charging installation in the world. This type of apparatus is best suited for the extremely difficult conditions in which such an installation must operate, particularly because of the high temperatures and because of the atmosphere laden with corrosive and abrasive dust.
In order to relieve the worst affected parts from these extreme conditions, an uncontrolled circulation of an inert gas under pressure and cooled in the annular chamber was initially provided in charging installations of this kind. This circulation possesses a double function, namely cooling the immersed parts by the cooling gas and preventing abrasive dust from entering the annular chamber because of the flow of inert gas towards the inside of the furnace through the labyrinths separating the fixed members from the rotary members.
More recently, U.S. Pat. No. 4,526,536, incorporated herein by reference, proposes replacing the system of cooling by uncontrolled immersion in an inert gas with a water cooling system consisting in cooling, in particular, the rotary cage by means of cooling coils. This cooling directly protects the wall of the rotary cage and reduces transmission, either by conduction or by radiation, of the heat to other parts, such as the bearings and gears for example.
Heretofore, no provision has been made also to cool the distribution chute. One of the reasons is that there has not been a pressing need for cooling of the chute, given that the operational temperatures of the upper parts of furnaces and the above-mentioned systems for cooling the drive device permitted satisfactory operation of the chute without necessitating direct cooling. However, the situation has changed in recent times through implementation of the powered coal injection processes, replacing the conventional oil-derived fuels. The use of these solid fuels results in a rise of the temperature in the central region of the furnace, with peaks which may exceed 1,000.degree. C. above the charging surface. These high temperatures reduce the strength of the anti-wear plates for protection of the chute, which results in an increase in the frequency of maintenance and of replacement and in a reduction in the mechanical strength of the chute.
Indeed, U.K. Patent GB-1,487,527, incorporated herein by reference, proposes a distribution chute having a double walled intended for a cooling system. This cooling system proposal was one for cooling by immersion, by connecting the chute cooling circuit through the chute suspension shafts to the annular chamber into which the inert gas was injected, with the aim that the cooling gas could spread as far as the inside of the chute. However, this proposal does not provide an effective cooling of the chute given that the inert gas penetrates only in a random manner into the chute cooling circuit, subject to the resistance which is offered to its passage. As it is, in order to be effective, the pressure of the inert gas inside the casing ought to be increased, but such an increase in the pressure would cause substantial leaks of gas through the labyrinths provided in order to contain it, and lead therefore, to an excessive consumption of gas.